In recent years, numerous advances have been made in the art of molding. Development of new molding techniques, compounds and material alloys for mold construction have steadily increased the level of technology. For example, various chromium plated alloys are now used to provide wear resistance to mold apparatus. One text entitled "Plastic Mold Design" by Bebb, published by the Plastics Institute in 1962, depicts in Chapter 5 a myriad of alloys available.
In the area of optical fiber connectors, however, the degree of precision required exceeds the tolerance limits available with existing molding techniques. One such optical connector, disclosed in a patent application to P. K. Runge, Ser. No. 630,930, filed Nov. 11, 1975, and assigned to the present assignee, discloses the use of a sleeve having a biconical aperture to precisely align two tapered male connector members. Each such male member contains an optical fiber.
For telecommunications applications, it is desirable for the optical losses through the optical connector to be less than 0.4 dB. To attain such limits, the total radial offset between each conical aperture in the sleeve must be equal to or less than 0.0001 inch (2.54.times.10.sup.-4 cm). Moreover, the end separation requirement between optical fibers must not exceed 30 microns (11.81.times.10.sup.-4 in). The molding of a biconical sleeve for such optical connectors, therefore, requires extreme precision on sleeve length and concentricity of the intersecting tapers.
The fabrication of a biconical aperture through the use of a two piece mandrel is known in the molding art. Such use is also disclosed, for example, in U.S. Pat. No. 3,314,266 to O. Werther et al, issued Apr. 18, 1967 for a method of making pipe coupling blanks. In Werther et al, two truncated tapered cylinders of revolution are inserted into each end of a coupling blank to size the internal diameter. The Werther et al method of making pipe coupling blanks is hardly suitable, however, for making an exceedingly precise biconical socket for optical fiber connector purposes.